Keep the evidence on a crash

Remove a scratch directory on a clean exit and keep it when the program crashed, by reading which door the program left by.

A handler is told how the program ended, so it can clean up differently for a crash than for a clean exit — remove a scratch directory normally, and keep it for the bug report when something was thrown.

scratch.mjs

import { mkdtempSync, rmSync } from 'node:fs';
import { tmpdir } from 'node:os';
import { join } from 'node:path';

import { onExit } from 'closeout';

const scratch = mkdtempSync(join(tmpdir(), 'build-'));

onExit(({ path, error }) => {
  if (path === 'uncaught' || path === 'rejection') {
    console.log(`kept the scratch directory: the build failed with "${error.message}"`);
    return;
  }
  rmSync(scratch, { recursive: true, force: true });
  console.log('removed the scratch directory');
});

if (process.argv[2] === 'fail') throw new Error('the compiler crashed');
console.log('built');

node scratch.mjs

built
removed the scratch directory

node --stack-trace-limit=0 scratch.mjs fail

kept the scratch directory: the build failed with "the compiler crashed"
[Error: the compiler crashed]

The handler runs on the throw path before the error is printed, and the process still exits 1 as Node would have. On exit — a process.exit() somewhere in the program — rmSync is the right call, because nothing can be awaited there: see Every exit path.